As individual identification technologies for identifying the identify of an individual such as an industrial product and a commercial product, various kinds are proposed and practically used; for example, a barcode, a serial number, and an IC tag. One of the individual identification technologies is a technology to form a layer containing fine granules on an object, extracting a feature quantity from an image obtained by imaging the layer, and setting the extracted feature quantity as an individual identifier of the object.
For example, Patent Documents 1, 2 and 3 describe techniques to use a taggant (an additive for tracking) as fine particles and form a layer containing the taggant on an object, take an image of a predetermined region of the layer and set the distribution of the particles in the predetermined region extracted from the image as a feature quantity (an individual identifier of the object).
To be specific, in Patent Document 1, a taggant distributed layer is formed entirely or partially on the surface of a reference object by applying printing ink containing a taggant, and a feature quantity extracted from an image obtained by reading the taggant distributed layer is set as an individual identifier of the reference object. At the time of verification of a target object, under the same conditions for reading such as orientation, position and range as those for reading the reference object, an image of a taggant distributed layer on the target object is read, and a feature quantity extracted from the image is compared with the individual identifier of the reference object.
Further, in Patent Document 2, an origin which becomes a fiducial point for positioning is set on each object, a feature quantity is extracted from a predetermined region of a two-dimensional plane on which a rightward direction from the origin is a positive direction of an X-axis and a downward direction from the origin is a positive direction of a Y-axis, and the extracted feature quantity is set as an individual identifier of the object.
Further, in Patent Document 3, a fiducial part is put on an object (the fiducial part is, for example, a positioning mark, a line, a company logo, a frame, and an edge or a combination of edges of the object), and a coating material containing a taggant, or the like, is sprayed and a random pattern is attached so as to cover at least the fiducial part. Then, a feature quantity depending on the distribution of the taggant is extracted from an image of the fiducial part and is set as an individual identifier of the object.    Patent Document 1: Japanese Unexamined Patent Application Publication No. JP-A 2013-069188    Patent Document 2: Japanese Unexamined Patent Application Publication No. JP-A 2014-006840    Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. JP-A 2007-534067
In the individual identification techniques according to Patent Documents 1 to 3 described above, a position and a range for extracting a feature quantity used as an individual identifier are defined for each object. The definition of the position and the range on an object varies with change of the outline and the size of an object. Therefore, application of the individual identification techniques according to Patent Documents 1 to 3 is limited to objects having the same outline and size, and it is difficult to generally apply the techniques to multiple kinds of objects having different outlines and sizes.